Hydraulic valve actuation systems have been employed to reduce fuel consumption in the last years. They use solenoid valves to couple a high pressure chamber with a lower pressure chamber. When the solenoid valve is open the actuation of the cams is not transmitted to the gas valves but simply circulates the hydraulic fluid in the hydraulic system. When the solenoid valve is closed the chambers are separated from each other establishing a hydraulic coupling between the camshaft and the gas exchange valves.
U.S. Pat. No. 7,954,464 discloses an electro-hydraulically controlled gas exchange valve actuation system. FIGS. 1, 3 and 5 of this patent are reproduced, with minor changes herein as prior art FIGS. 5, 6 and 7 in order to illustrate the known components typically found in the cylinder head of an internal combustion engine with such valve actuation systems. In FIG. 5, a cylinder head 11 of an internal combustion engine is shown having a top 12, under which an electrohydraulic valve control unit 13 is located having a plurality of electrically controllable hydraulic valves 14, which are preferably solenoid valves. The hydraulic medium filling port 15 and filling device 16 are also shown along with an end of the camshaft 17. A cylinder 18 associated with one set of valves is also indicated
FIG. 6 is a detail from U.S. Pat. No. 7,954,464 showing the master unit 22 which includes a cam follower 24 supported in an articulated manner on a rigid support element 23 with a roller bearing-supported roller 25 as the cam pick-up surface and also a spring-loaded pump piston 26, which is driven by the cam follower 24 and which limits a variable volume pressure space 27. The lower housing part 19 is constructed as a pressure-sealed, forged part made from aluminum. For an opened hydraulic valve 14, the pressure space 27 is connected to a pressure relief space 28, which is limited, on its side, by a spring force-loaded piston 29 of a pressurized storage device 30. A sensor 31 screwed into the lower housing part 19 is used for detecting the hydraulic medium temperature.
Prior art FIG. 7 shows the hydraulic valve 14, which is also arranged offset to the associated master unit 22 and slave unit 34 in the longitudinal direction of the hydraulic unit 13. The slave unit is shown acting on a gas exchange valve 35, whose stem contacts the slave unit 34. The channel 32 is connected to another channel hydraulically by an annular groove 39 running on the hydraulic valve 14, so that the annular groove 39, just like the connected channels, is a component of the pressure space 27. In the opened state, the hydraulic valve 14 permits an overflow of hydraulic medium from the pressure space 27 into the pressure relief space 28 and back via a borehole 40 connecting the pressure relief space 28 to the annular groove 39.
Sometimes the solenoid valves get stuck and cause misfire in the engine. This may happen if they get stuck in the closed or the open position. There are control circuits that check upon the electric current in the coil of the solenoid valves and evaluate whether the valve got stuck or not. This usually takes a long time exceeding several engine cycles and impairs the overall performance. When trying to reduce the malicious effects the detection becomes unreliable.
In DE 103 24 807 A1 the main idea is the detection of misfire, but also a statement regarding the solenoid valves could be made since the respective signals are combined in an AND-comparator. The problem is that not all known misfire detection methods are combinable with this teaching, which also does not allow to further improve the certainty of the prediction.